Drag modification piezoelectric panels

ABSTRACT

Disclosed is a method and means to increase or decrease, on demand, the drag exerted by a fluid on a boundary. The boundary comprises a surface portion of a structure enclosing a moving fluid or may comprise a portion of the outer surface of an object moving through the fluid. Drag is varied by means of a set of piezoelectric sensors and an accompanying set of piezoelectric driver elements arranged in close proximity to one another at the boundary and electrically interconnected so that the pressure exerted by the moving fluid is sensed by one or more sensors and converted to an electrical signal which is then transformed into an electrical drive signal which is applied to one or more driver elements to cause a flexing of the driver element(s) in a predetermined direction so that drag is either reduced by moving the driver(s) away from the fluid or increased by moving the driver(s) towards the fluid. In the case of turbulent flow, drag is decreased by decreasing the pressure gradient in the fluid; that is, the drivers are moved away from the fluid in regions of high pressure and toward the fluid in regions of low pressure. The drag is increased by reversing these motions.

FIELD OF THE INVENTION

The present invention relates to a method and means for reducing thedrag exerted by a fluid on a surface and more particularly to a methodand means whereby piezoelectric elements are utilized to actively detectthe motion of the fluid on a boundary surface and in accordance with thesensed condition causing a motion of the boundary surface to respond byeither moving the boundary area toward or away from the fluid flow asdesired.

In the past much effort has been expanded in the study of therelationship between fluid drag and the motion of a boundary surface;however, none of the prior efforts have attempted to tie the motion ofthe boundary surface to the fluid motion except passively by using acompliant surface.

Accordingly, it is an object of the present invention to provide anactive system for varying the motion of the boundary surface of a movingfluid in response to the motion of the fluid.

It is another object of the present invention to use piezoelectricmaterials to reduce fluid drag.

A further object of the present invention is to provide drag reductionof fluid flow by reducing the pressure exerted by the fluid on a surfacewhere it is high while raising the pressure where it is low.

SUMMARY

Briefly, the subject invention is directed to the method and apparatusfor reducing fluid drag on a boundary surface through which or overwhich a fluid moves by piezoelectrically sensing the pressuredistribution which controls the drag on the boundary, amplifying theresulting electrical signal, selectively operating on the phase of theelectrical signal by a predetermined magnitude and then applying theamplified phased signal to piezoelectric material which is caused toflex in a predetermined direction whereby movement away from the fluidwill reduce pressure while movement toward the fluid will increasepressure at the area of concern.

These and other objects will become more apparent when the followingdetailed description is considered in view of the accompanying drawings.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustrative diagram of a piezoelectric sensor-driver arrayin accordance with the preferred embodiment of the subject invention;

FIG. 2 is an electrical schematic representation of one piezoelectricsensor-driver combination utilized in the array shown in FIG. 1;

FIG. 3 is an electrical block diagram for one type of electrical circuitfor operating a particular sensor-driver combination;

FIG. 4 is a diagram illustrative of a piezoelectric sensor-driver arrayin accordance with another embodiment of the subject invention;

FIG. 5 is an electrical schematic diagram of one sensor-drivercombination utilized in the array shown in FIG. 4;

FIG. 6 is a partial perspective view of a fluid conduit which is adaptedto utilize the subject invention;

FIG. 7 is a partial perspective view of another type of conduit which isadapted to utilize the subject invention;

FIG. 8 is an electrical schematic diagram of a second type of electricalcircuitry utilized for operating the sensor-drivers of the subjectinvention;

FIG. 9 is an electrical block diagram of a third type of electricalcircuit for operating the sensor-driver of the subject invention;

FIG. 10 is a diagram illustrative of another form of utilization for thesubject invention; and

FIG. 11 is a diagram illustrative of yet another form of utilization ofthe subject invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As noted above, the purpose of the subject invention is to increase ordecrease, on demand, the drag exerted by a fluid on a boundary surface,which boundary may be part of a structure enclosing a moving fluid or itmay be part of the outer surface of an object moving through the fluid.The apparatus by which the drag is varied consists of a set ofpiezoelectric sensors and drivers arranged in such a fashion at theboundary surface that a particular sensor is adapted to operate arespective driver or a group of drivers or alternatively a group ofsensors collectively operate a single driver or a group of drivers. Forsake of simplicity and clarity, however, the subject invention will bedescribed in terms of a single piezoelectric sensor being used inconnection with a respective piezoelectric driver.

To this end reference will now be made to the drawings and moreparticularly to FIG. 1 wherein reference numeral 10 designates acompliant base member in the form of a panel which is separated into aplurality of resilient or flexible generally rectangular sections 12,each of which accommodates a piezoelectric sensor element 14 mounted inpiggy-back fashion on a piezoelectric driver element 16. Accordingly, anarray of sensor-drivers is provided on the panel 10. As shown in FIG. 1,the sensor 14 is relatively smaller than the driver 16 and is generallycircular in configuration whereas the driver is of a generallyrectangular configuration.

The piezoelectric sensor-driver configuration of each section of thearray is shown schematically in FIG. 2. The preferred construction foreach sensor 14 is a combination of two sheets 18 and 20 of piezoelectricmaterial cemented face to face and oppositely polarized with respect toone another such that when the element 14 is subjected to pressure, thecommon interface 22 provides a charge of the same polarity while bothouter faces 24 and 26 generate a charge of the opposite polarity. Inlike fashion, the preferred construction for each driver element is acombination of two sheets of piezoelectric material 28 and 30 cementedin face-to-face relationship, however, they have a like mutual polarityi.e. in the same direction, such that when their outer faces 32 and 34are connected together and a signal is applied to their common interface36, one sheet expands while the other contracts, causing the combinationof both layers 28 and 30 to flex in the same direction as determined bythe polarity of the applied signal. When desirable a single sheetconfiguration may be utilized.

However, in the embodiment disclosed both the outer faces 24 and 26 ofthe sensor element 14 are connected together via an electricalconnection 37 while the outer faces 32 and 34 of the driver element 16are connected together by means of electrical connection 38.Furthermore, both electrical connections 37 and 38 are adapted to beconnected to a point of reference potential, commonly referred to asground.

Accordingly, with the piezoelectric sensor configuration 14 cemented tothe upper surface 26 of the driver element 16 and an electrical circuitconnection 40 being made to the sensor interface 22 while an electricalconnection 42 is made to the driver interface 36 a structure resultswhich can sense the pressure exerted on the panel 12 whereupon anelectrical signal appears on circuit lead 40 which is coupled to theinterface 22. The pressure can then be counteracted or increased bymeans of applying a drive signal generated from the sensor signal tocircuit lead 42 connected to the interface 36 of the driver 16. Wherethe pressure exerted comprises the drag exerted by a fluid in contactwith the sensor 14, the electrical signal produced on circuit lead 40would be coupled to electrical circuitry such as shown in FIG. 3 wherebythe signal appearing on circuit lead 40 is amplified, altered in phaseif desired or necessary, and reapplied to circuit lead 42 which causesthe driver element 16 to flex in one direction or another depending uponthe result desired, i.e. moving an area of the boundary away from thefluid will reduce pressure at that area while moving the area toward thefluid will increase the pressure at that area.

In its simplest form, the circuitry required to implement such afunction is shown in FIG. 3 and includes inter alia, means foramplifying and selectively adjusting and varying, if need be, the phasebetween the sensor signal and the signal applied to the driver. Saidcircuit means includes a signal phase shifter 44 coupled to the outputof a signal amplifier 46 connected between the sensor element 14 and thephase shifter. In addition to the phase shifter 44, which comprises avariable phase shifter, there is included 180° phase shifter circuit 48and a by-pass signal path 50 which, respectively, provides a reversedphase and a substantially in-phase driver signal being applied to thepiezoelectric driver 16 depending upon the setting of the switch 52. Inorder to provide additional amplification of the signal to the driverelement 16 an additional amplifier 54 is provided; however, whendesirable, it may be eliminated where the gain of the input amplifier 46is sufficient to provide the necessary amplification to the signal beingapplied to the circuit lead 42.

Thus drag can be reduced by moving the driver 16 away from the fluid inthe region of a high pressure and toward the fluid in a region of lowpressure as dictated by signal output of the sensor 14 on the circuitlead 40. This particularly is pertinent for turbulent flow where drag isa function of pressure gradient. Alternatively, drag can be increasedsimply by reversing these motions. For example, where the switch 52connects the variable phase shifter 44 to the 180° phase shifter 48, thepiezoelectric driver 16 will operate to flex away from pressure whereasthe condition of the switch 52 whereby the by-pass circuit 50 is coupledto the variable phase shifter 44 the driver element will move toward theregion of pressure. In both cases the variable phase shifter 44 providesa means for adjusting the relative phases of the signals such thatsubstantially zero or 180° phase shift exists between the output of thesensor 14 and the input to the driver 16.

While the configuration as disclosed in FIGS. 1 and 2 discloses what isat present considered to be the preferred embodiment of the invention,another embodiment thereof is shown in FIGS. 4 and 5. There 10'designates a compliant panel member having a plurality of flexiblerectangular sections 12' which are adapted to accommodate an arrangementof alternating sets of piezoelectric elements of sensors 14' and drivers16'. The respective drivers 14' and 16' are generally of a rectangularconfiguration of substantially the same size. As shown in FIG. 5, eachsensor element is comprised of piezoelectric sheets 18 and 20 cementedin face-to-face relationship as the sensor element 14 shown in FIG. 2and having the same relative polarity while the driver element 16' iscomprised of piezoelectric layers 28 and 30 as before. In thisconfiguration, the sensor-driver pair are not in piggy backconfiguration but are mounted side-by-side with their respective outerfaces connected together to ground potential while the inner face 22 ofthe sensor element 14' has an output circuit lead 40 connected theretowhile the inner face 36 of the driver element 16' is connected to aninput circuit lead 42. The array of sensor-driver elements 14' and 16'shown in FIG. 4 is operable in the same fashion by means of, forexample, circuitry shown in FIG. 3; however, it exhibits one limitationin that only the sections 12' containing the driver element 16' wouldflex in response to pressure being sensed by the adjacent sensors 14'.

Nevertheless, the two embodiments of the invention provide a meanswhereby the motion of a fluid and the motion of the boundary surface canbe actively linked together for modifying the drag exerted by the fluidon the boundary surface. To this end FIGS. 6 and 7 disclose two forms offluid conduits of a generally rectangular and circular cross section,respectively, which contain inner boundary surface areas defined by oneor more piezoelectric sensor-driver panels 10 as shown in FIGS. 1 and 4suitably operated, for example, by circuitry shown in FIG. 3. Individualelectrical connections provide no great problem, inasmuch assemiconductor integrated circuit chips or other such elements can bereadily fabricated by one skilled in the art to operate variouspiezoelectric elements either individually or in groups. Further, underdifferent conditions of fluid composition, fluid flow, relative speedand boundary shape, the relative pressure distribution may be thepressure at the center of the specific areas under consideration, thepressure at the upstream edge of the area under consideration, thepressure at some distance upstream, the pressure grading across thearea, or some combination thereof. What is significant is that thepanels 10 provide a boundary surface area which is actively operable tomove away from fluid so as to reduce the pressure at that area oralternatively, can move toward the fluid and thus increase the pressureat that area.

While the circuitry shown in FIG. 3 is a relatively simple means ofoperating a particular sensor-driver pair, in instances where high speedfluid motion is encountered, it may be desirable to anticipate pressurevalues by differentiating the sensor signal and employing a circuitconfiguration such as shown in FIG. 8 whereby in addition to thevariable phase shifter 44 and the 180° phase shifter 48 as well as theby-pass circuit arrangement including the circuit lead 50 and switch 52,coupled between the input amplifier 46 and the power amplifier 54, adifferentiator circuit 60, a second variable phase shifter 62 andanother 180° phase shift circuit 64 and a by-pass circuit 66 and switchtherefor 68. Both signal channels feed into a signal summer circuit 70where a composite signal is formed for driving the piezoelectric element16.

The circuitry shown in FIGS. 3 and 8 are illustrative of two circuitconfigurations whereby a piezoelectric driver element 16 is driven inresponse to the signal generated solely by a piezoelectric sensorelement 14, it being noted, however, that when desirable a plurality ofpiezoelectric driver elements can be driven in response to the signalgenerated by a single sensor or alternatively, a single driver elementcan be driven in response to the sensor signals generated by one or moreindividual sensors. The circuitry in FIG. 9, however, is intended toillustrate yet another circuit configuration for operating apiezoelectric sensor-driver combination wherein the sensor 14 isutilized to provide a negative feedback signal from the driver 16 whichoperates in response to a command signal provided, for example, by meansof a variable DC supply circuit 72. Such a combination additionallyincludes a signal mixer 74 whereby the signal inputs from the sensor 14and the DC power supply 72 are algebraically summed, i.e. subtractedfrom one another in a negative feedback sense to provide an error signalto the variable phase shift circuit which is adapted to cause the driver16 to operate in such a manner that the feedback signal provided by thesensor 14 will act in a servo mode whereby a zero error signal willoccur. In such a mode the driver 16 is caused to follow the variation ofthe DC bias supply 72. The circuitry in FIG. 9 also includes aresistance-capacitance averaging network 76 which has an RC timeconstant sufficiently large to provide a smoothing effect for aturbulent eddy, for example, to pass the sensor 14.

A circuit such as shown in FIG. 9 has particular utility in certainapplications where it is desirable to vary the drag of fluid movingaround an external surface, a typical example of which is the hull of aship as shown in FIG. 10 and the air foil surfaces and/or fuselagesurface of an air craft as shown in FIG. 11. With respect to FIG. 10,reference numeral 76 designates a ship, for example, which includes atleast one piezoelectric sensor-driver panel 10 of predetermined size andnumbers positioned on either side of the aft portion of the hull 76below the water line. Where, for example the array of sensor-driverelements on one side operates to increase the drag, while thecorresponding array on the other side of the hull reduces the dragthereat, a steering effect is achieved which may be utilized whendesirable to either complement the conventional steering mechanism or bysuitable design, can be implemented to provide the sole means ofguidance. While not shown, other additional piezoelectric sensor-driverpanels 10 can be located on the hull, for example in the forward portionthereof, to provide a drag modification surface for the sea waterpassing the hull at that particular location.

With respect to the configuration shown in FIG. 11, a plurality ofpiezoelectric sensor-driver panels 10 are selectively located along thewing surfaces 78, the elevator surfaces 80 and over a predeterminedportion of the fuselage section 82. Such an arrangement is purely one ofillustration in that more than one panel 10 can be applied at anylocation where drag of air flow over any outer surface of the air craftcan be varied as desired. Where, for example, panel members 10 arelocated on the upper and lower surfaces of the wing and operated in sucha fashion that the drag is increased on one surface panel whiledecreased on the other surface, the lift over the wing surface can bemodified to provide either a guidance function or a trimming function ora combination of both. While not so evident, piezoelectric sensor-driverpanels 10 can be applied to upper and lower portions of the fuselage 82and operated in mutually opposite senses to provide the same effect.

Accordingly, what has been shown and described is a method and apparatusby which drag on an area is varied by: piezoelectrically sensing thepressure distribution which controls the drag on the area of interest,suitably amplifying the electrical signal produced by the sensing stepand where applicable thereafter differentiating the amplified signal,varying the phase of the sense signal, if necessary, to substantially beeither in phase or 180° out of phase with the sense signal andthereafter applying the phased signal to a piezoelectric driver elementto cause a flexing of the boundary surface at the sensed area and/oradjacent vicinity to move either toward or away from a fluid moving overthe boundary surface and thereby increase or decrease, as the case maybe, the drag exerted by the fluid on the boundary.

While the foregoing detailed description has been described with acertain degree of particularity, it is to be noted that such has beenpresented by way of illustration and not by limitation and accordinglyall modifications, alterations and changes coming within the spirit andscope of the present invention as defined by the appended claims areherein meant to be included.

I claim:
 1. The method of modifying the drag exerted by a fluid on aboundary surface, comprising the steps of:sensing effect of the dragexerted by the fluid on said boundary surface; generating an electricalsignal which is a function of the drag sensed; modifying the electricalsignal in a predetermined manner for energizing an electricalenergizable movable element at said boundary surface; and applying saidmodified electrical signal to said movable element at said boundarysurface which is energized thereby and selectively moves toward or awayfrom said fluid to modify the fluid drag exerted on said boundarysurface.
 2. The method as defined by claim 1 wherein said sensing stepcomprises sensing by means of a piezoelectric sensor element thepressure exerted by the fluid on the boundary surface.
 3. The method asdefined by claim 2 wherein said step of applying comprises applying saidelectrical signal to a piezoelectric driver element which is operable toflex bi-directionally toward or away from said fluid in response to saidmodified electrical signal.
 4. The method as defined by claim 3 whereinsaid piezoelectric sensor element and said piezoelectric driver elementare located in close proximity to one another.
 5. The method as definedby claim 4 wherein said step of modifying the electrical signal includesamplifying said electrical signal generated as a function of the dragexerted.
 6. The method as defined by claim 4 wherein said step ofmodifying the electrical signal comprises selectively adjusting thephase of said electrical signal for causing said driver element to movetoward said fluid.
 7. The method as defined in claim 4 wherein said stepof modifying comprises altering the phase of said electrical signal formoving said driver element away from said fluid.
 8. The method asdefined by claim 4 wherein said step of modifying comprisesdifferentiating said electrical signal which is adapted to anticipatepressure exerted by a fluid having a relatively high speed of motionover said boundary surface.
 9. The method as defined by claim 1 whereinsaid sensing step comprises sensing the drag exerted by fluid on aninner boundary surface of a fluid conductive structure.
 10. The methodas defined by claim 1 wherein said step of sensing the effect of thedrag comprises sensing pressure exerted by the fluid on the outersurface of an object moving through said fluid.
 11. Apparatus formodifying fluid drag on a boundary surface, comprising incombination:first piezoelectric means for sensing the effect of dragexerted by a fluid on said boundary surface and being operable togenerate an electrical signal in accordance with the drag sensed;electrical circuit means for transforming said electrical signalgenerated by said first piezoelectric means into an electrical drivesignal capable of energizing piezoelectric means; and secondpiezoelectric means coupled to said drive signal and being energizedthereby and becoming flexed to cause said boundary surface to move in apredetermined direction relative to said fluid and thereby modify thedrag exerted thereby.
 12. The apparatus as defined by claim 11 whereinsaid boundary surface comprises a compliant surface and said secondpiezoelectric means is located on said compliant surface.
 13. Theapparatus as defined by claim 12 wherein said first piezoelectric meansis also located on said compliant surface.
 14. The apparatus as definedby claim 13 wherein said first and second piezoelectric means arecomprised of separate piezoelectric elements, each consisting ofsandwiched layers of piezoelectric material.
 15. The apparatus asdefined by claim 14 wherein said first piezoelectric element iscomprised of at least two layers of piezoelectric material which arebonded together in a mutually opposite electrical polarity relationshipwhereby a common polarity electrical signal is generated at the innerface thereof in response to a pressure exerted by said fluid on saidboundary surface.
 16. The apparatus as defined by claim 14 wherein saidsecond piezoelectric element comprises at least two layers ofpiezoelectric material bonded together in mutually like polarityrelationship whereby electrical drive signal coupled to the inner facethereof causes a flexing of both piezoelectric layers in the samedirection.
 17. The apparatus as defined by claim 14 wherein said firstand second piezoelectric elements are mounted in a piggy-backarrangement on said boundary surface.
 18. The apparatus as defined byclaim 11 wherein said first and second piezoelectric means comprises afirst and second set of piezoelectric sensor and driver elements,respectively, located on said boundary surface.
 19. The apparatus asdefined by claim 18 wherein said boundary surface comprises a compliantboundary surface having a plurality of individual surface sections andwherein each section includes at least one piezoelectric element of saidfirst and second sets of piezoelectric elements.
 20. The apparatus asdefined by claim 19 wherein said each surface section includes onesensor element and one driver element.
 21. The apparatus as defined byclaim 20 wherein said electrical circuit means comprises individualcircuit means coupled between a selected sensor and driver elementlocated on each surface section.
 22. The apparatus as defined by claim21 wherein said sensor and driver elements are mounted on top of oneanother on said surface section.
 23. The apparatus as defined by claim11 wherein said electrical circuit means includes circuit means foraltering the electrical phase of said electrical signal generated bysaid first piezoelectric means to cause said boundary surface to moveaway from said fluid.
 24. The apparatus as defined by claim 11 whereinsaid electrical circuit means includes signal amplifying means and phasealteration means, said phase alteration means being adapted to move saidboundary surface in said predetermined direction relative to the dragexerted by said fluid on said boundary surface.
 25. The apparatus asdefined by claim 11 wherein said electrical circuit means includessignal amplifying means and signal differentiating means.
 26. Theapparatus as defined by claim 11 wherein said first and secondpiezoelectric means comprises respective sets of piezoelectric elementslocated on first and second flexible panel members affixed to oppositesides of a structure moving through said fluid and wherein said circuitmeans comprises means coupled to said first and second sets ofpiezoelectric elements whereby drive signals applied to the secondpiezoelectric elements of said first panel moves said first panel in afirst direction relative to said fluid and the second piezoelectricelements of said second panel moves said second panel in a seconddirection relative to said fluid to provide a steering effect of saidobject.
 27. The apparatus as defined by claim 26 wherein said objectcomprises a vehicle moving through a liquid.
 28. The apparatus asdefined by claim 26 wherein said object comprises a vehicle movingthrough a gaseous medium.